Joint effects of daily events and dispositional sensitivities to cues of reward and punishment on daily positive affect (PA) and negative affect (NA) were examined in 3 diary studies. Study 1 showed that positive events were strongly related to PA but not NA, whereas negative events were strongly related to NA but not PA. Studies 2 and 3 examined how the dispositional sensitivities of independent appetitive and aversive motivational systems, the Behavioral Activation System (BAS) and the Behavioral Inhibition System (BIS), moderated these relationships. Participants in Study 2 with higher BAS sensitivity reported more PA on average; those with more sensitive BIS reported more NA. Also, BIS moderated reactions to negative events, such that higher BIS sensitivity magnified reactions to negative events. Study 3 replicated these findings and showed that BAS predisposed people to experience more positive events. Results demonstrate the value of distinguishing within-person and between-person effects to clarify the functionally independent processes by which dispositional sensitivities influence affect.